The present invention relates to the field of transmitting radiofrequency signals, and it relates more particularly to a device for transmitting radiofrequency signals, the device comprising power amplifier means for amplifying the power of a radiofrequency signal received at an input of said power amplifier means, and gain control means for controlling the gain of said power amplifier means to regulate said gain in such a manner that the power of the output signal from said power amplifier means tends towards a desired nominal value.
In a telecommunications system connecting a mobile terminal to a base station, it is necessary to guarantee a minimum quality of service. For example, when transmitting digital signals, this condition requires that the binary error rate should always be less than some specified rate. To satisfy this condition on reception, it is ensured that the received signal-to-noise ratio exceeds a predetermined value at all times.
The problem which the invention seeks to solve is that of allocating a power resource to each call from the terminal to the base station which is dedicated thereto, such that said power is just sufficient for the signal-to-noise ratio to satisfy specifications. This ensures that calls have a required quality of service guaranteeing a binary error rate below a predetermined limit while avoiding excessive power consumption. The transmitted power needs to be only just sufficient because of the limited amount of power available in the terminal.
To enable the power of the signal for transmission to be raised, the mobile terminal is provided with a power amplifier. During a call, this power amplifier is used to transmit at a power level that is sufficient to enable the corresponding base station to receive properly, given the specifications in force. For example, when said base station is at a distance from the terminal such that it receives little or no more call information from the terminal, the station sends a message to the terminal to transmit at some higher level of power as determined by the station.
A correspondence table, e.g. recorded in a memory of the terminal, establishes a correspondence between this power level to be transmitted and a predetermined value. The signal to be transmitted is input to the power amplifier, and a loop then monitors the signal output by the power amplifier in order to compare it with said predetermined value. Until this value is reached, the comparator acts on the power amplifier to cause it to increase its output power.
Unfortunately, the way in which a power amplifier increases its output power varies from one amplifier to another depending on the particular components constituting it, on the drift to which it might have been subject, . . . .
Nevertheless, this state of affairs must comply with timing characteristics defined in specifications and stipulating limits within which the rise in amplifier power must lie. Thus, if power rises too slowly, then information can be lost, whereas if power rises too quickly then that will occupy a large amount of spectrum which will be detrimental to the calls of other terminals.
Consequently, from the above, it can be seen that in prior art terminals, the length of time it takes to raise the power from a power amplifier is not only undeterminable, but it can also be too long to guarantee that the required quality of service is complied with.
An object of the present invention is to remedy the problem as posed above at the terminal, and it seeks to reach the desired power level quickly following a stimulus of the input signal at the determined input of the power amplifier.
To this end, the invention provides a device for transmitting radiofrequency signals, the device comprising power amplifier means for amplifying a power of the radiofrequency signal received at an input of said power amplifier means, and gain control means for controlling the gain of said power amplifier means to regulate said gain in such a manner that the power of the output signal from said power amplifier means tends towards a desired nominal value, said gain control means operating on a monitoring signal representative of a measurement signal giving the output power from said power amplifier means, in order to deliver a gain control signal for controlling variation in the gain of the power amplifier means, wherein, in addition to the power amplifier means, said device further comprises adjustment means that are responsive to said gain control signal to deliver an additional adjustment signal to the gain control signal in such a manner that the monitoring signal, which is also representative of the adjustment signal, is suitable for causing said gain control means to respond more quickly.
Thus, the device of the invention with adjustment means other than the prior art regulation loop and reacting more quickly to the signal input to the power amplifier makes it possible to reach a desired power level for transmission more quickly. The transfer function of the power amplifier is modified for this purpose.
In an embodiment, the adjustment means comprise only passive components. Thus, the responses to an input signal stimulus can drift only very little, whereas said usual control means have active elements whose responses are liable to drift.
In an embodiment, the adjustment means comprise a resistor bridge.
In an embodiment, the adjustment means comprise an integrating RC circuit.
In an embodiment, the device of the invention is integrated in a digital appliance belonging to the group {mobile telephone; digital personal assistant; portable computer}.